海南岛东南部海湾潟湖沉积和碳埋藏变化研究

SEDIMENT ACCUMULATION AND CARBON BURIAL IN TWO TROPICAL LAGOONS, SOUTHEASTERN HAINAN ISLAND

本文选择海南岛东南部热带小型海湾为研究区,探讨热带珊瑚礁生态系统对海岸碳埋藏的贡献,以及小流域系统物质循环过程对极端风暴事件和人类活动的响应.对来自海南岛东南部黎安和新村潟湖的柱状祥和表层底质样品,在室内进行了粒度、有机碳、无机碳和210pb年代指标测试和分析.结果表明,新村潟湖有机碳和无机碳含量均较高于黎安潟湖,新村潟湖有机碳埋藏速率（9× 105 kg/a）为黎安潟湖有机碳埋藏速率（3× 105kg/a）的3倍.珊瑚礁生态系统对于这两个潟湖碳埋藏具有重要贡献.新村潟湖柱样岩芯XC-06无机碳含量在1980～2000年期间存在急剧锐减的趋势,可能与同期该地养殖和过度捕捞致使珊瑚礁生长受限有关.根据沉积物物质守恒原理和沉积物来源分析,海南岛频繁的台风风暴事件对于新村和黎安潟湖沉积的实际贡献远大于总量的1/3.在未来人类活动和台风活动呈现上升态势背景下,该地区碳埋藏量将进一步发生变化.海南岛小流域海湾、潟湖碳埋藏量可以达到108～ 109kg/a量级,接近于海南近陆架有机碳通量（2× 109 kg/a）,表明海湾潟湖对于本区浅海碳埋藏具有重要贡献.

The Xincun and Li-An lagoons are located on the southeastern coast of Hainan Island, China, and the geomorphology here is characterized by tidal channels/inlets, tidal marshes, coastal dunes and marine terraces. Before the 1980s, these coastal embayments were characterized by a rich biodiversity of coral reefs, seagrass and mangroves. Recently, however, these ecosystems have been extensively interfered by human activities （e. g., agriculture, aquaculture and tourism） and damaged by natural events （e.g. storms and typhoons）. These two small tropical sedimentary basins were investigated to understand their sediment infilling and carbon burial patterns in response to tropical extreme storms and anthropogenic processes. Surficial sediment samples and 7 short cores were collected and analyzed to obtain data sets of grain size, organic and inorganic carbon contents, deposition rates, vertical fluxes of sediment and organic carbon. The results obtained show that the lagoons are covered by mud deposits with high organic and inorganic carbon contents. Both organic and inorganic carbon contents in sediments from the Xincun lagoon are higher than those from the Li-An lagoon. The organic carbon burial rate （9× 106kg/a） in the Xincun lagoon is some 3 times higher than that in the Li-An lagoon （3 × 106 kg/a）. Provenance analysis indicates that the higher carbon burial in Xincun may have resulted from the larger-area distribution of coral reefs. Likewise, the sharp decline of inorganic carbon contents in Xincun during 1980～2000 may be related to dramatic decrease of coral reefs, which suffer greatly from global warming, overfishing and eutrophication. In addition, sediment accumulation and carbon burial of the two lagoons are affected significantly by typhoons. In Xincun, approximately 1.33×107kg/a of sediments were transported to the tidal basin by the typhoon-induced rainfall, which accounts for a third of the total sediment deposition （4.64× 107kg/a）. Increased typhoon activities may enhance silicate weathering rates and exacerbate sediment loads, thereby increase organic matter and sediment burials in the tidal basins. Hence, the impacts of typhoon on sediment transport and carbon burial need further studies. Furthermore, the organic carbon fluxes from these two lagoons and other embayment along the Hainan Island coastlines demonstrate that tropical coastal embayments make an important contribution to the regional patterns of shallow marine carbon burial. The burial rate of organic carbon of the major （17） embayment on the coast of Hainan Island reaches 0.34 × 108 kg/a. The total carbon burial rate would reach an order of magnitude of 108- 109kg/a. Such a quantity is not small compared with the value （2×109kg/a） for the adjacent continental shelves near Hainan Island.